The present invention is directed to the field of DPSK detectors and more particularly to a DPSK detector which utilizes a circulating memory. Detection of differentially encoded phase shift keyed (DPSK) signals by a receiver has been accomplished by comparing the received DPSK signal against a local carrier signal generated in the receiver. A comparison is generally made by utilizing a phase detector circuit wherein the received DPSK signal and the local carrier signal are compared in phase and an output signal, which is a function of the difference in phase between the two compared signals, is provided. In order to receive valid phase information the local carrier signal must be synchronized to the carrier signal component of the received DPSK signal. A phaselock loop can be used to control the phase of the local carrier signal so as to achieve synchronization. In order to reduce the time required for the phaselock loop to lock to the local carrier signal of the received DPSK signal quicker methods of accomplishing detection were developed. Lock up time has been reduced by implementing a DPSK detector so as to compare the phase of adjacent bit periods of the received signal. Such a detection scheme must be capable of storing energy for a bit period, so that it may be compared with the next received bit. In comparing the phase of a previously received bit against a recently received bit a phase reversal can, for example, indicate a "MARK" (1 bit) and the absence of a phase reversal can indicate a "SPACE" (0 bit).
Integrate and dump filters are used to integrate for a period of time equal to one information bit a down converted form of the received DPSK signal. The down converted signal is designated an IF signal. At the end of each information bit time period the filter is dumped and the integration process begun anew. By sampling the output signal from the integrate and dump filter at the information bit rate a determination can be made as to whether there is a phase difference between information bits.